It is desirable to produce elastomeric compounds exhibiting reduced hysteresis. Such elastomers, when compounded to form articles such as tires, power belts and the like, show an increase in rebound and a decreased rolling resistance and display less heat build-up when mechanical stresses are applied.
Previous attempts at preparing reduced hysteresis products have included high temperature mixing of the filler-rubber mixtures in the presence of selectively reactive promoters to promote compounding material reinforcement; surface oxidation of the compounding materials; chemical modifications to the terminal end of polymers using tetramethyldiaminobenzophenone (Michler's ketone), tin coupling agents and the like and, surface grafting thereon. All of these approaches have focused upon increased interaction between the elastomer and the compounding materials.
It has also been recognized that carbon black, employed as a reinforcing filler in rubber compounds, should be well dispersed throughout the rubber in order to improve various physical properties. One example of the recognition is provided in published European Patent Application EP 0 316 255 A2 which discloses a process for end capping polydienes by reacting a metal terminated polydiene with a capping agent such as a halogenated nitrile, a heterocyclic aromatic nitrogen containing compound or an alkyl benzoate. Additionally, the application discloses that both ends of the polydiene chains can be capped with polar groups by utilizing functionalized initiators, such as lithium amides.
U.S. Pat. No. 5,153,159, to Antkowiak et al, discloses an anionic polymerizing initiator formed by the reaction product of a functionalizing agent selected from the group consisting of substituted aldimines, ketimines and secondary amines, and an organolithium compound. These initiators are used to prepare elastomeric polymers having functional sites at the initiator end of the polymer chain and exhibiting reduced hysteresis, however their use produces undesirable side effects. Since these functionalizing agents initiate polymerization from a nitrogen atom initiation rates are low and termination reactions occur that promote undesirable branching. Furthermore, only batch polymerization techniques can be employed utilizing the nitrogen atom initiated polymerizations since lower reaction temperatures must be maintained to limit side reactions.